This is by far the best of the numbered series of Star Trek novels up to the point at which it was written, with the possible exception of #7, "The Wrath Of Khan". The characters are handled competently, the plot is interesting, and the writing is fluent, professional, and lively.
There is a certain similarity between the plot of this story, and the plot of "Star Trek VI: The Undiscovered Country", but that is no fault of this story, since it predates the other. There is also a certain similarity between its plot and that of "Dr. Strangelove", although this is not a comedy. This story is set in the time immediately after the original series Star Trek episode, "Tomorrow Is Yesterday"; the computer has not yet been reprogrammed, and is still overly affectionate toward Kirk.
If you enjoy Star Trek: the original series, you should definitely read this book; it is one of the better books in the Star Trek series. Even if you aren't a big fan, but are only lukewarm toward Star Trek, you should give this book a try.